1. Field
Example embodiments relate to a light emitting diode (LED), and more particularly, to an LED emitting a light beam having improved polarization characteristics.
2. Description of the Related Art
Light emitting diodes (LEDs) have been used widely in signal devices and advertisement devices in electronic, electric, and communicational fields. For example, LEDs have been used in transportation devices, flashlights, displaying devices, brake lamps, and signboards. LEDs are eco-friendly devices because they do not use mercury (Hg), and have lower power consumption due to their lighter weight. In addition, because LEDs have relatively longer lifetime and higher reliability, it is expected that LEDs will replace conventional lightings. Also, because the driving circuits for LEDs are simpler and controlling R/G/B color signals may be easier, LEDs may be used in digital lightings and back light units (BLUs).
Recently, cold cathode fluorescent lamps (CCFLs) have been used as backlight units in liquid crystal displays (LCDs). In addition, because an LCD needs to use a polarized light beam, a polarizer may be disposed on front and rear surfaces of a liquid crystal layer. However, because a light beam emitted from a CCFL is not polarized, about 50% of the light beam emitted from the CCFL may not be used to display an image and may be absorbed by the polarizer or other devices. In order to overcome this problem, a dual brightness enhanced film (DBEF) has been primarily used. Prom the light beam emitted from the CCFL, the DBEF transmits a light beam polarized in a particular direction and reflects a light beam polarized in a perpendicular direction. The reflected light beam may be polarized in order to be transmitted through the DBEF by using an optical material, e.g., a diffuser or retarder. Thus, a ratio of a light beam that is used to display an image with respect to a light beam emitted from the CCFL that is not polarized may be increased. That is, light usage efficiency may be increased. However, the DBEF may be expensive.
A backlight unit including an LED may have longer lifetime and smaller power consumption compared to a backlight unit including a CCFL. In addition, a backlight unit including an LED may realize higher contrast by local dimming, may realize 100%-NTSC color reproduction, and may efficiently control image quality by a rapid response velocity. In addition, because LEDs controlling polarization do not require DBEFS, active research has been conducted on the LEDs. However, a current LED formed of (In)GaN in a film type generates a light beam that is not polarized. Thus, in order to control the polarization of an LED, a polarization state of a reflective light beam may be changed by disposing a polarizer on a light emitting unit, stacking a plurality of layer structures, e.g., DBEFs, or placing a double-refracted material below the light emitting unit. However, when the double-refracted material is placed below the light emitting unit, forming a metal contact for an electrode on the light emitting unit may be difficult.